Abstract: Geographic information systems are very important vehicles running on Information Superhighawy and serve many different users with geo-spatial data. The two characters of GIS are technology-driven and application-oriented. With the rapid development of computer technique, communication technique, space positioning technique, remote sensing and visualization technique GIS hardware and software environment and the methods of spatial data acquisition, storage, access, analysis, representation and visualization will be improved continually and rapidly. Facing this situation the author try to think about geographic information theory. Main discussion in this paper includes:optimal representation of spatial data with attribute data in computer, automatic acquisition and updating of spatial data, spatial data quality and uncertainty, spatial query and analysis of GIS data, visualization symbolization and multi-scaling representation of spatial data etc. On the discussion we pay more attentions to compare and to distinguish the differences between computer based GIS and paper map based "analogue GIS" and to consider the developing tendency of tomorrow's computer technique and information science.